Sub-pixel regions on the faceplate of a flat panel display are typically separated by an opaque mesh-like structure commonly referred to as a black matrix. By separating sub-pixel regions, the black matrix prevents electrons directed at one sub-pixel from being "back-scattered" and striking another sub-pixel. In so doing, a conventional black matrix prevents helps maintain a flat panel display with sharp resolution. In addition, the black matrix is also used as a base on which to locate structures such as, for example, support walls.
In one prior art black matrix, a very thin layer (e.g. approximately 2-3 microns) of a conductive material is applied to the interior surface of the faceplate surrounding the sub-pixel regions. Typically, the conductive black matrix is formed of a conductive graphite material. By having a conductive black matrix, excess charges induced by electrons striking the top or sides of the black matrix can be easily drained from the interior surface of the faceplate. Additionally, by having a conductive black matrix, electrical arcs occurring between field emitters of the flat panel display and the faceplate will be more likely to strike the black matrix. Such arcing is of particular concern in high voltage environments. By having the electrical arcing occur between the black matrix and the field emitters instead of between the sub-pixels and the field emitters, the integrity of the phosphors and the overlying aluminum layer is maintained. Unfortunately, due to the relatively low height of such a prior art conductive black matrix, arcing can still occur from the field emitter to the sub-pixel regions. As a result of such arcing, phosphors and the overlying aluminum layer can be damaged. As mentioned above, however, the black matrix is also intended to prevent back-scattering of electrons from one sub-pixel to another sub-pixel. Thus, it is desirable to have a black matrix with a height which sufficiently isolates each sub-pixel from respective neighboring sub-pixels. However, due to the physical property of the conductive graphite material, the height of the black matrix is limited to the aforementioned 2-3 microns.
In another prior art black matrix, a non-conductive polyimide material is patterned across the interior surface of the black matrix. In such a conventional black matrix, the black matrix has a uniform height of approximately 20-40 microns. Thus, the height of such a black matrix is well suited to isolating each sub-pixel from respective neighboring sub-pixels. As a result, such a black matrix configuration effectively prevents unwanted back-scattering of electrons into neighboring sub-pixels. Unfortunately, prior art polyimide black matrices are not conductive. As a result, even though the top edge of the polyimide black matrix is much closer than the sub-pixel region is to the field emitter, unwanted arcing can still occur from the field emitter to the sub-pixel regions. In a prior art attempt to prevent such arcing, a conductive coating (i.e. indium tin oxide (ITO)) is applied to the non-conductive polyimide black matrix. ITO coated non-conductive black matrices are not without problems, however. For example, the high atomic weight of ITO results in unwanted back-scattering of electrons. Furthermore, ITO has a undesirably high secondary emission coefficient, .delta..
Additionally, coating non-conductive black matrices with a layer of ITO commonly results in the deposition of ITO on the faceplate in the sub-pixel regions. As a result, a layer of ITO layer underlies subsequently deposited phosphors. Due to the high index of refraction of the ITO material, light emitted from the phosphors can be reflected away from the faceplate, thereby reducing the emission intensity of the flat panel display.
Thus, a need exists for conductively coated black matrix structure which effectively separates neighboring sub-pixels. A further need exists for a conductively coated black matrix structure which does not have the increased back-scattering rate, and the undesirably high secondary emission coefficient associated with an ITO coated black matrix structure. Still another need exists for a conductively coated black matrix structure which does not result in the formation of a highly reflective layer in the sub-pixel regions of a flat panel display.